1. Field of the Invention:
The present invention relates to emulsifiable, liquid, homogeneous, one phase phenolic resole resins and to emulsions prepared therefrom using an emulsifying agent, such as a proteinaceous compound, in combination with the resole resin.
2. Description of the Prior Art:
The concept of phenolic resins emulsions is in general well known in the prior art and such emulsions have been recommended for use in impregnations and binder applications for binding fibers in the form of felts or sheets of fibers, such as non-woven fiber mats.
Non-woven fiber mats are typically manufactured by a process known as "wet" process. This process is well known in the art, and as typified by the disclosure in U.S. Pat. No. 4,129,674. Inorganic fibers are commonly used in fiber mats. Glass fibers, mineral wool and carbon fibers are examples of such inorganic fibers. Further, fibers of various sizes may be blended together to form the mat. See, for example, U.S. Pat. No. 4,637,951 to Gill et al. and U.S. Pat. No. 4,129,674 to Hannes et at. It is also known that mineral wool may be partially or wholly substituted for glass wool (i.e. glass fibers) in a blended mat. See, for example U.S. Pat. No. 4,532,006 to Winters et al. Ultimately, the fibers in the wet process mat are bonded to each other using chemical binders such as urea-, phenol-, or melamine-aldehyde condensation resins. Preferably, the fibers are bonded using a cured phenol-formaldehyde resin. The binder may also contain filler materials such as clay and gypsum among others. See U.S. Pat. No. 5,001,005 to Blanpied.
The properties desired of binder compositions depend to a large extent on the properties of the basic resin. A good binder composition should above all be easily applied and capable of covering and/or bonding the fibers, and at the same time it should cause little pollution. Further, the resin should have good long term stability and a high degree of dilutability with water. Since the concept of dilutability is particularly important, it will be defined for the purposes of the present invention as follows: The water dilutability of a resin solution is the volume of deionized water which can be added at a given temperature to one unit volume of this solution without producing any permanent perturbation, i.e., haze, clouding or precipitation.
Of particular interest are high efficiency single phase aqueous phenol-formaldehyde resins which have low free phenol, low free formaldehyde and low saligenin (ortho-hydroxybenzyl alcohol). Such resins retain a high percentage of the organic moiety when the resin is cured. However, the free phenol, free formaldehyde and saligenin volatilize in the curing of the resin causing pollution considerations and also reducing the efficiency and performance of the resin in various bonding applications. Accordingly, it is necessary that the resin should be as free as possible from any unconverted starting materials or residues thereof while preserving its useful qualities. The risk of atmospheric pollution is in fact mainly due to the presence of volatile monomers. These consist, for example, the starting materials required for producing the resin, e.g. formaldehyde and phenol, which have been left unconverted by the reaction or regenerated in the course of binding the fibers or subsequently.
A high efficiency resin is extremely valuable to the industry since it results in a greater economic advantage over conventional resins. Even more important is the increase in performance of the resin in bonding applications. However, in addition to the problems dealing with unconverted starting materials, another of the unfortunate drawbacks with a high efficiency single phase aqueous phenol formaldehyde resin is the instability of the resin which results in the formation of a solid or crystal phase. This crystal phase is extremely difficult to dissolve and prevents uniform application of the resin to a substrate.
As is well known in the art, the normal base catalyzed addition reaction of formaldehyde with phenol produces via methylolation a mixture of five mono-,di-, and tri-methylolated phenol monomers which are potential intermediates for dimer formation via condensation. In dimerization of these methylolated phenols, the formation of bis (4-hydroxy-3,5-dimethylolphenyl) methane is favored and when the ratio of formaldehyde to phenol is high, i.e., when it is above 2.0, substantial amounts of bis (4-hydroxy-3,5 -dimethylolphenyl) methane (i.e., tetradimer) is formed. Even when the proportion of tetradimer is relatively low and methylolated phenols are in relatively high concentrations, the tetradimer crystallizes out from conventional resoles when the formaldehyde content is below 3 percent and the pH is adjusted to less than 8.5, particularly at pH in the range of 6 to 8 and at low temperatures in the range of about 0.degree. to about 20.degree. C., preferred for storage. See U.S. Pat. No. 3,956,204 to Higginbottom. This crystal phase is extremely difficult to be dissolved. Heating the resin to elevated temperatures helps to re-dissolve the crystal phase, but unfortunately, such exposure to high temperatures will also advance the resin, increasing its molecular weight and decreasing its water tolerance, so that its application performance is adversely affected. Filtering out the crystals is of little benefit because the resulting resin is reduced in efficiency and the bonding characteristics are impaired. Moreover, the economics of the process become unfavorable and a problem of disposing tetradimer is created.
The prior art regarding the manufacture of phenolic resole resins has concentrated on preventing the formation of tetradimer or treating the resole resin to stabilize the tetradimer formed.
U.S. Pat. No. 3,428,593 maintains the stability of the resole system by the addition of formaldehyde after manufacture. This resole is water soluble. The mechanism for maintaining solubility and storage stability in this system is to use free formaldehyde at a level of approximately 3% to prevent the tetradimer from precipitating. Under current environmental considerations and limitations, such a system is unacceptable due to the high content of free formaldehyde which would evolve during curing. Additionally, to maintain water solubility, the phenolic species are predominately in the monomer form (i.e., trimethylolated phenol). Such is also problematic with regard to emissions of low molecular weight components during curing.
U.S. Pat. Nos. 3,956,204; 3,956,205; and 4,060,504 require an acid condensation step and use of an alkali of a divalent cation in the methylolation step to limit the formation of tetradimer. This results in the formation of dimers with open para positions which are more reactive yet do not form crystalline precipitate like tetradimer. However, these more reactive species pose stability problems at elevated temperatures (i.e., 5.degree. to 25.degree. C.) as they tend to further react during storage with the resulting materials settling out.
U.S. Pat. No. 4,480,068 and Canadian 1,080,871 disclose water soluble phenolic resoles prepared using basic catalysts having an alkaline earth metal divalent cation, i.e. calcium. The resulting resin has a low molecular weight as it is predominantly monomers for imparting water solubility. However, higher emissions of phenolic species are expected during curing. The divalent cation catalysts also favor the formation of dimers with open para positions and the resulting resoles likewise suffer from the associated instability problems at elevated temperatures (i.e., 5.degree. to 25.degree. C.). Further, the divalent cations also interfere with emulsification in that they tend to couple or bridge and agglomerate anionic species, e.g. phenolic species.
U.S. Pat. No. 3,862,060 discloses the production of phenolic resin emulsions. The process utilizes amine catalysts during condensation and aminotriazines in the methylolation step to increase water insolubility. That is, the resin has such a low tolerance for water that it is emulsified on manufacture at high solids. U.S. Pat. No. 3,862,060 also enumerates problems associated with utilizing alkali metal catalysts and teaches away from their use.
U.S. Pat. No. 4,663,419 discloses phenol formaldehyde resoles with urea addition catalyzed with sodium hydroxide. The resoles thereof are water soluble and are dilutable in water to at least 1,000%. In example 3 thereof, the resin was infinitely dilutable. The resole resins disclosed therein are prepared using a specific temperature cycle having three phases: a heating phase, a phase during which the temperature is maintained, and a cooling phase. Urea is added during the cooling phase, preferably during the first half of the cooling phase. The cycle does not exceed seven hours in duration. Further, the phase during which the temperature is kept constant is limited to at most about 90 minutes. Example 1 provides an example when the temperature is maintained at 70.degree. C. for about 71 minutes and in example 2 the temperature is maintained at 70.degree. C. for 90 minutes.
Additionally, various methods aimed at reducing the volatile monomer content present in such compositions based on a phenoplast resin have been proposed. The principle of these methods is based on the idea of increasing the initial molar ratio of formaldehyde to phenol in order to lower the uncombined and consequently free phenol content and at the same time bind the free formaldehyde present in excess by means of nitrogen compounds, in particular urea. See, for example, U.S. Pat. No. 3,616,179 wherein phenol, formaldehyde and urea are simultaneously charged to the reactor and reacted together and U.S. Pat. Nos. 3,684,467 and 4,014,726 wherein phenol, formaldehyde and dextrine or dicyandiamide (formaldehyde scavengers) are simultaneously charged to the reactor and reacted together with urea added during the cooling phase of the reaction. U.S. Pat. No. 4,480,068 to Santos et al. discloses that a variety of special binder systems have been designed for use in mineral fiber insulating material adapted to withstand high temperatures. These resins are phenol-formaldehyde resins which are modified with nitrogen-containing compounds, such as urea, dicyandiamide and melamine in various combinations. See U.S. Pat. Nos. 3,624,246 and 3,956,204. However, U.S. Pat. No. 4,480,068 notes that these nitrogen modified resins, for the most part, are difficult to manufacture, and have poor storage stability, short gel times and poor processability.
A need therefore exists for high efficiency stable single phase, phenolic resole resins which contain low concentrations of phenol and aldehyde such as formaldehyde, and thus cause substantially less pollution of the atmosphere than prior art resins. A further need exists for such resins in emulsifiable form so that they maybe used to prepare stable high efficiency phenol formaldehyde emulsions for impregnation of sheet members and fibrous substrates and as binders for fibrous mats, wherein the fibers are of organic and/or inorganic origin.